The present invention is directed to machine tools, and more particularly to apparatus for automatic coil feed of a sheet metal stock strip in progressive dies for punch press die operations which assures that the correct length of stock strip is intermittently fed to the punch press die while the press is in an operating mode.
It is the usual practice in automatic coil feed of sheet metal stock strip for punch press die operations to automatically feed a predetermined length of stock strip to the punch press die for punch operations such as pierce punching of holes through the metal stock strip. Such apparatus, however, is often unable to continuously feed the correct predetermined length of stock strip because of various conditions involving the punch press operation and the metal stock strip being fed to the punch press. For instance, there may be buildup of dirt and oil on the stock strip, variations in temperatures under which the punch press is operating and gage variations of the sheet metal stock strip or other coil imperfections, all of which either alone or in various combinations cause a drift in the accuracy of the feed length of the stock strip for punch press die operations.
As disclosed in U.S. Pat. No. 2,986,254, heretofore in fabricating machines such as in a machine for cutting portions of a predetermined length off the end of a strip as it is intermittently advanced to a cutting tool, feeler members have been utilized to engage the sheet metal stock strip and if the stock strip is improperly positioned a pin engaging a spring loaded actuator of a switch is cammed such that the switch is opened and that switch renders the machine inoperative. This type of machine control is deficient in that the machine operation is shut down and an operator must make the adjustments to the machine or coil feeding apparatus to again realign the metal stock strip correctly and re-initiate operation of the machine. This results in a considerable amount of machine down time and manual labor to correct the misalignment. Other misfeed detectors for machine tools such as disclosed in U.S. Pat. No. 3,124,026 use a device in conjunction with a pilot punch to detect misfeed and terminating operation of the apparatus for manually correcting the feed length.
It is also known to control the length of feed of a web processing machine wherein apparatus is utilized to cut in individual zones on the web must be fed properly and positioned relative to a cutting blade at a predetermined time. Such an arrangement is shown in U.S. Pat. No. 3,739,968 wherein there is a means of detection and correction of potential misregistration by a control system that detects the position of a particular register mark with respect to the cutting blade at a given point in time and the operating cycle of the blade. If it appears that the register mark is in registry, no correction signal is sent by the control system to the correction motor. However, if misregistration is indicated and correction is required, the control system provides an appropriate control signal to the correction motor to momentarily change web-feed length. The control system of this patent is an electronic type of scanner and is not a mechanically operating sensing means that cooperates with the downward movement of the punch press to perform a punching operation.
By this invention, there is provided a means for automatically adjusting the length of stock strip being fed to the punch press die and the automatic adjusting may take place while the press is in an operating mode. Moreover, the apparatus for detecting and controlling overfeed or underfeed of the stock strip is cooperatively arranged with the punch press and operates in unison therewith.